Modulators, voltage controlled oscillators, and other devices employing varactors have been previously proposed for use in RF applications. A varactor is a device whose capacitance varies with the voltage thereacross. One of the criteria that dictates the design of a varactor for RF applications, particularly for RF wireless applications, is the capacitive switching ratio R. The capacitive switching ratio R is defined as Cmax/Cmin, where Cmax is the maximum capacitance of the varactor, and where Cmin is the minimum capacitance of the varactor.
FIG. 1 is a graph showing the capacitance response of a typical varactor, where capacitance is given along the y-axis and voltage is given along the x-axis. As can be see by the graph of FIG. 1, the capacitive switching ratio of a typical varactor is on the order of 2 to 2.5.
Such a low capacitive switching ratio has limited both the tuning range and the quality factor Q of known varactors. However, higher capacitive switching ratios have been difficult to attain, particularly in RF wireless applications where power consumption is of necessity kept as low as possible.
The present invention is directed to a varactor that is arranged to attain a higher capacitance switching ratio R than that described above.